composer - 'glow' animation for icons

Alright, so I just started playing with composer two days ago. I have successfully created a svg which basically replicates the default bottom dock icons in theme builder. When off focus there is a light background square and when on focus the square is black with a highlight around it.

What I want to do now is have the icon 'glow' when it first comes in focus then fade out. Similar to the default action in theme builder.

My thought process is to just make a white rectangle layer which fades out over a second. I have done that, BUT how the heck do you do it when each icon goes on focus!? I can get it to work but the animation plays only when simulator starts and then never again. The rest of the svg works as it did before.